This invention relates to radio frequency transmitters and to power output devices for use therein.
Particularly in radio navigation systems, the phase of the radiated signal has to be controlled accurately. If solid state technology is to be used in high power transmitters, it is necessary to use a large number of drive circuits and, considered from one of its aspects, the present invention is directed to an improved form of power output device enabling a large number of solid state current control units to be used to provide a high voltage, high power radio frequency output.
The invention finds particular application in the transmission of pulses of radio frequency in such a manner that an individual cycle in a pulse can be identified. Such pulse signals are required, for example, in the radio navigation system known as Loran C, in which radio frequency transmissions are made from a number of spaced transmitters in sequence. The transmissions each consist of short duration pulses of radio frequency energy with a predetermined waveform and with the radio frequency cycles within the pulses from the different stations held in a fixed phase relationship. Coarse positional information may thus be obtained by determining, at a receiver, the time differences between received pulses but it is also possible to obtain more accurate positional information by determining the phase relationship between the radio frequency signals from spaced stations.